JP2003-517328(A) discloses an ultrasonic diagnostic apparatus for evaluating a bone using ultrasonic waves. The ultrasonic diagnostic apparatus emits an ultrasonic pulse and receives an ultrasonic wave which is propagated in a cortical bone and emitted from the cortical bone. Then, the ultrasonic diagnostic apparatus measures a period of period of time from the time of transmitting the ultrasonic wave to the time of receiving the same, and finds speed-of-sound in the cortical bone from a propagation path known.
Since the speed-of-sound in an object varies depending on the elastic property of the object, measurement of speed-of-sound in the bone can be used for an index of bone strength (health of the bone). The ultrasonic diagnostic apparatus of JP2003-517328(A) uses the speed-of-sound obtained as above as an evaluation value of the bone.
In a case of a configuration where a time interval from the time of transmitting the ultrasonic pulse wave to the time of receiving the same is measured by a timer like in the case of JP2003-517328(A), a peak of the pulse of the received wave must be adequately detected from among waveform signals outputted by a transducer. Here, in a case of an ideal condition (for example, measurement of an object located in water), it is relatively easy to detect the pulse of the received wave. However, in an actual measurement using a living body as a subject, since fat and water are mixed in the propagation path of the ultrasonic wave, various noises are generated, for example, an unnecessary echo is generated, an unnecessary waveform is superimposed due to the reflection from a back surface of the cortical bone and the like.
As for this point, in the configuration of JP2003-517328(A), if the noises are contained in the waveform signal from among the waveform signals, it becomes difficult to detect the necessary pulse of the received wave, and it has not been possible to stably measure the period of time from the time of transmitting the ultrasonic pulse wave to the time of receiving the same ultrasonic pulse. Therefore, if an examination of the bone strength is tried on the actual site, an accurate result is difficult to obtain and there remains room for improvement.